I am currently building an autonomous sensor node, sending temperature & humidity over a 433 mhz transmitter.
The sensor node is to be battery powered.
There is no lack of documentation for such a system.
I have sourced several cheap 8mhz/3.3v arduino pro mini off ebay, $2 items.
I currently am powering the device through 4 AA batteries in a battery holder.
I wanted to use the sleep power down mode to reduce battery payload.
It does work, going into sleep power down for 10 minutes, sending correct temp, humid, voltage.
And that's where things start being funny.
I have a fully functionnal setup, with 433mhz transmitter & dht22 wired, power led desoldered on arduino board. It sends data for 4 days before running out of juice (2500mah nimh).
I have hooked a (also cheapish, $15 this time) multimeter on battery wire, in order to have a current reading.
Found several things.
Arduino mini, full system with sensor & TX, powered through vcc pin (5v, a bit high I understand)
Arduino running (setup, and everything before sleep power down command is issued) : 18 milliamps
Arduino sleeping power down, about 8 milliamps.
Powering the same setup through RAW pin (to my knowledge, that sends the 5v provided to the internal voltage regulator).
16 mA running, 2.5 mA in sleep power down.
Board must be fried or loaded with a funny thing, or I did cause some harm desoldering the cms led ?
Let's try with a brand new arduino mini pro 3.3v out of the bag (a $2 item off ebay, also).
No sensor, no nothing, power led still attached. Naked board.
Let's boot it with the same code.
Through RAW pin, 13mA running, 5mA in sleep power down.
Through VCC pin, 32 mA running, 13mA in sleep power down.
I tried different soft ways (rocket lib & direct code) without any change noticed.
That's the moment when soldering iron & multimeter are stored, and I start the browser to write a post. This post.
What I do not get is why a loaded board eats way more, and why going through regulator ends up in less power sipped.
Next steps are :
- A different kind of arduino mini pro ($4 off ebay this time, whoooooohoooo)
- A two cells battery holder (in case 4 AA nimh voltage is the cause, but i did try with lower voltage by inserting a cable between battery & spring holder without any success regarding consumption)
- A bigger battery holder.
- Solar charging setup.
- Self contained nuclear power plant.
- Heavy battery setup.
- Edit : I may have one arduino mini left in a bag. I'll try this one too...
I do not wish to build an award winning setup, I just wish I could have something that eats comething under 1 milliamp in power down, in order to be able to power it through C/R14 sized alkaline batteries.
Did anyone encounter a arduino mini clone stubbornly refusing to enjoy quiescent power levels ?